Effect of Dicyandiamide Nitrification Inhibitor on Maize Yield and Soil Nitrate Levels in Four Field Studies.

Commercial maize (zea mays) production usually requires nitrogen fertilizer inputs, in addition to nitrogen from organic matter mineralization, in order to obtain optimal yields. However, nitrogen not taken up by the crop can be subject to loss, primarily through volatilization, leaching and denitrification. Stakeholder concern over the environmental impact of leached nitrogen from fertilizer inputs coupled with the desire to optimize nitrogen use efficiency has led to inclusion of the nitrification inhibitor dicyandiamide (DCD), in some nitrogen fertilizer applications. A survey of four replicated field trials, located in Oregon USA, Louisiana USA, Nebraska USA, and Madrid Spain indicates that DCD can significantly reduce the concentration of soil NO3-N during the growing season. In the two studies that directly measured soil NO3-N, the concentration of soil NO3-N in the DCD-treated plots was approximately one third less than the standard reference N-fertilizer (SRF) source. However, the inclusion of DCD in nitrogen fertilizer did not universally result in an increase in yield. In two of the four studies, grain yield was statistically equivalent for DCD-treated N-fertilizer compared to the SRF. One study demonstrated statistically greater yield in the DCD-treated N-fertilizer compared to the SRF, and in the fourth study the DCD-treated fertilizer treatment resulted in statistically greater yield than the SRF in one of three nitrogen rates applied. The use of DCD provides the potential to reduce soil NO3-N concentrations, which could result in reduced incidents of leaching or denitrification, but may not always result in an increase in grain yield.